The erosion-accumulative activity of water flows occurs on different spatial scales at different levels of catchment erosion-fluvial systems (CEFS). The article presents the main results of studies carried out by the scientific school of the Makkaveev Laboratory of Soil Erosion and Fluvial Processes at Moscow State University. These studies are devoted to the main components of CEFS – slopes and interfluves, river channels, as well as sediment runoff connecting these spatially separated zones of the river basin. Each of the research areas is characterized in terms of the most relevant technologies – physical models and models of shared contribution, balance approaches applicable to interfluves; the method of hydrodynamic modeling of channel flows; sediment runoff monitoring technologies. Data are presented on the intensity of erosion-accumulative processes on the slopes of temperate watersheds and estimates of sediment delivery from watersheds of different sizes to the river network. This article examines methods for studying river floodplains, their formation and evolution, and mapping principles, as well as practical aspects of floodplain development and the mapping of economic activity within them. Using the largest river basins in the Russian Federation (the Ob, Yenisei, Lena, and Kolyma) as examples, it is shown that under modern hydroclimatic conditions, these areas are accumulation zones, where the sediment load transported outside the river basin is significantly lower than the sediment mass transported by erosion processes in the catchment area and river channels.

The article presents the results of a comprehensive study aimed at improving navigable conditions in the limiting section of the Irtysh River in the Semey area (Upper and Lower Zhanasemeisky ridges, 2900-2904 km of navigation). The research is based on the methodology of hybrid (combined) hydraulic modeling, which integrates numerical calculations in the HEC-RAS software package and experiments on a spatial physical model. The purpose of the work is a comparative analysis of the effectiveness and justification of the parameters of two variants of regulating hydraulic structures (longitudinal and transverse dams) to ensure guaranteed depths during the inter–ice period. Verification of the numerical model and calibration of the physical model based on field observations were carried out. It was found that both options provide a significant increase in water levels (up to 92 cm for the longitudinal and up to 62 cm for the transverse dam) at an intermediate flow rate of 625 m3/s. A negative effect in the form of a cross-jet flow (up to 1.5 m/s) was identified and quantified for the option with a longitudinal dam, which required correction of its position. Using a semi-collapsible physical model, morphodynamic processes during the flood period (flow rate of 3500 m3/s) were studied and areas of potential erosion threatening the stability of structures were identified. Engineering measures to protect against erosion (reinforcement with flexible reinforced concrete mats and boulder filling) have been developed and tested on the model for each variant. The complementarity and high efficiency of combining numerical and physical modeling methods to obtain reliable and integrated engineering solutions are proved.

The paper presents the results of comprehensive studies of the hydromorphological regime of the Lower Volga at two sites: the tailrace of the Cheboksary HPP and the VolgaCaspian Sea Navigation Canal. For the first time, longterm hydrological and channel observations (from 1877 to the present) are combined with mathematical modeling data. Methods of correlationregression analysis, water level exceedance probability assessment, and comparison of channel survey plans are used. It is established that in the tailrace of the Cheboksary HPP, after 40 years of operation, the intensity of erosion has decreased to 1.1 cm/year, and the correlation of water levels between the gauges “HPP tailrace” and “Kozlovka village” is 0.927, indicating the absence of irreversible water level lowering associated with the development of channel quarries. On the VolgaCaspian Canal, it is shown that the lowering of the Caspian Sea level provokes accelerated transformation of the canal into a river channel with the formation of riffles, side bars, and dune bedforms, leading to increased siltation and necessitating larger dredging volumes. The obtained results are of practical importance for planning dredging operations, optimizing hydropower release regimes, and locating spoil disposal sites.

The paper represents the analysis of the geographic-hydrological approach in the study of river channel formation conditions, their morphology and dynamics. It provides a historical overview and assesses the role of N.I. Makkaveev in the creation of the study and associated scientific school. It substantiates the importance of the geographic-hydrological approach in the development of the theory of channel processes (channel studies) and the solution of related applied problems. Its relationship with the hydromorphological theory of channel processes (GGI), hydrodynamic and hydraulic engineering approaches is demonstrated. The following base contributions of the channel processes study are considered in detail: mechanisms and forms of manifestation of channel processes on lowland, semi-mountain and mountain rivers; river runoff and water regime as leading factors of channel processes (small and large rivers); geological and geomorphological conditions of channel formation (free and limited development of channel changes); sediment flow and composition; vertical channel deformations (incision and accumulation of sediments); morphodynamic types of channels, their diversity and their evolution; ridge movement of sediments and formation of channel bottom relief; river floodplains both as product and factor of channel processes; paleochannel analysis and forecasting of channel changes under hydroclimatic changes and anthropogenic impacts; channel processes as a component of erosion-fluvial systems.